Discrimination of the specific neuropsychological deficits occurring with chronic low-level exposure to different neurotoxic substances and development of a conceptual framework to explicate the mechanisms of these effects are of primary importance in the field of behavioral neurotoxicology. These issues are particularly germane to individual health and welfare as knowledge about them will allow development of screening techniques and preventive health measures aimed at minimizing the neurological, behavioral, social, and safety hazards which may accompany neurotoxic exposures. This three-year study will test a group of workers exposed to a little-investigated group of mixed solvents to be compared with non-exposed workers. Following medical, neurological, and demographic screening, each worker will undergo a short (60-75 minute) battery of neuropsychological tests, including a standard screening battery and additional tests of cognitive flexibility. Retesting will be completed at 12-month intervals. Research design is modeled after that used in a study on lead-exposed workers in order to maximize comparability of data collected on solvents to existing data on lead. The present investigation will utilize traditional neuropsychological methodology to examine the specific cognitive deficits which may accompany chronic exposure to this group of mixed solvents, assess relationship of duration of exposure to degree and nature of neuropsychological deficits, examine changes in test performance within subjects over time, and explore the nature of cognitive flexibility in workers with this exposure. Comparisons will be made between the neuropsychological data on this population and those derived from the parallel completed study of lead workers in order to discriminate specific cognitive and affective characteristics of lead and solvent encephalopathies. These discriminations may provide clues in explicating the mechanisms (psychologic, neuropathologic, metabolic) underlying specific neurotoxic encephalopathies. In particular, tasks assessing cognitive flexibility are included to determine whether cognitive rigidity may be contributing to the functional intellectual deficits accompanying exposure to these solvents and to gain further information about brain behavior relationships by examining effects of this exposure on tasks known to be sensitive to cerebral frontal lobe dysfunction.